(1) Field of the Invention
The present invention relates to processes used to fabricate semiconductor devices, and more specifically to a process used to detect particles in a semiconductor fabrication tool, prior to operation of this tool.
(2) Description of Prior Art
Micro-miniaturization, or the ability to fabricate semiconductor devices comprised with sub-micron features, has been achieved via advances in specific semiconductor disciplines, such as photolithography and dry etching. The development of more advanced exposure cameras, as well as the use of more sensitive photoresist layers, have allowed sub-micron features to be achieved in photoresist layers. In addition the development of more advanced dry etching tools, and processes, have allowed the sub-micron features in the masking photoresist shapes to be successfully transferred to underlying materials, such as metal layers used for the interconnect structures of sub-micron, semiconductor devices. However the yield of semiconductor devices can be adversely influenced during the above patterning procedure, (photolithography and dry etching), due to the presence of unwanted particles present in the dry etching chamber. The particles in a dry etching chamber, in the form of polymer residues, formed during previous dry etching procedures, can settle on a exposed region of metal layer, masking this region during the dry etching procedure, resulting in bridging between subsequent, adjacent metal interconnect structures. In addition the unwanted particle can settle on the location of the electrostatic chuck, (ESC), of the dry etching tool, in which the semiconductor wafer is to be placed prior to etching. This in turn results in poor contact between the wafer and ESC, decreasing heat transfer from the wafer to the chuck, during the dry etching procedure, thus resulting in hot spots, or damage to the masking photoresist shape, again leading to unwanted metal interconnect patterns.
A majority of methods used to determine particle counts in a dry etching system can only be performed during the dry etching procedure, therefore only predicting metal interconnect yield loss during the etching cycle, but unable to alleviate the present situation. This is a result of a particle warning procedure only operational, when the plasma used to etch the exposed metal layers, gas already been generated. One such procedure of this type is a backside helium alarm system. With the type of procedure the wafers to be etched reside on openings in ESC, with helium fed to these openings allowing wafer cooling to be accomplished via heat transfer from the wafer backside to helium. If a particle were present on this portion of the ESC the wafer would not sit flush on the ESC, allowing helium to escape from the opening between the wafer and the ESC, resulting in the monitoring of helium in the dry etch chamber, and suggesting particle contamination in the dry etching tool. Unfortunately the procedure of introducing helium is only available in the presence of a plasma, which means that in addition to the indication of particles the dry etching procedure has already begun to define an unwanted metal interconnect pattern.
This invention will describe a backside helium alarm procedure in which only a first cycle of a dry etching procedure is needed to initiate the helium alarm procedure, with the first cycle comprised of dry etching conditions which do not initiate the definition of metal interconnect pattern. This allows the dry etching procedure to be suspended, during this non-etching, first cycle, allowing the desired metal interconnect pattern to be defined after particle cleanup, and possible photoresist rework. Prior art, such as Weiling et al, in U.S. Pat. No. 5,522,957, describe a method for leak detection, however that prior art does not describe the novel procedure used in the present invention of detecting particles in the dry etching system, in the presence of a mild plasma, however with the particle detection occurring prior to initiation of the metal interconnect definition procedure.